1. Field of the Disclosure
The present invention relates generally to photodetectors, and more specifically, the present invention is directed to silicon photomultipliers.
2. Background
A silicon photomultiplier (SiPM) is one type of photodetector that is capable of detecting a low intensity signal, as low as a single photon. SiPM devices can be used in a variety of applications including for example detecting ionizing radiation or scillintation. SiPMs are semiconductor photosensitive devices made up of an array of Geiger-mode photon detection cells such as avalanche photodiodes (APDs) that are fabricated on a silicon substrate. Geiger-mode APDs produce a pulse of the same amplitude when struck by a photon. They have a p-n junction that is biased above the breakdown voltage such that each electron-hole pair can trigger an avalanche multiplication process that causes current at the output of the photon detection cell to reach its final value quickly. This avalanche current continues until a quenching element is used to quench the avalanche process. Each photo detection cell is an individual photon counter and all photon detection cells are connected in parallel. The output of the SiPM is the sum of all the photon detection cells processed by a readout circuit and is proportional to the input photon pulse.
There are many factors that may affect the timing resolution of a SiPM. As the physical sizes of the photosensitive devices in the array of photon detection cells in the SiPM increase, the different signal propagation delays caused by the different distances between the photon detection cells in the SiPM and the readout circuit cause unwanted skewing, which degrades the timing resolution.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.